1. Field of the Invention
This invention relates to construction of a seal arrangement for the sliding part of a pin slide type disc brake.
2. Description of the Prior Art
The conventionally known disc brakes of this type include a disc brake of construction wherein a support is arranged to have a vertical flat face portion disposed in parallel with a rotating face of a disc rotor on one side thereof and a horizontal flat face portion extending from this vertical flat face portion across the edge portion of the disc rotor in the axial direction to the other side of the rotor; a main slide pin which slidably engages a cylindrical portion of a caliper having one end thereof open is supported by the vertical flat face portion of the support in a cantilever like manner; and an auxiliary slide pin is either arranged similarly to this or the auxiliary slide pin is fixed to the caliper while a member which is arranged to slidably engage with the auxiliary slide pin is fixed to the support. The present invention relates to a sealing structure arrangement for the sliding part of a disc brake of the type allowing a slide pin to engage with such a one-end-open cylindrical portion of a caliper assembly.
In a disc brake of this type in general, there is normally provided a boot for the purpose of securing the slidability between the cylindrical portion and the slide pin by shutting off their sliding faces from outside air to prevent muddy water etc. from entering there. The boot is attached to the edge of the open end of the cylindrical portion and has one end part arranged to be airtightly slidable on the outer circumferential surface of the slide pin and the other end firmly fixed to the outer circumferential surface of a part of the slide pin at which the slide pin does not slidably engage the cylindrical portion, the boot thus being arranged to be extendable and contractible in the axial directions. With the boot mounted in this manner, the sliding engagement part of the disc brake is ensured to maintain sufficient slidability between the slide pin and the cylindrical portion thus by a double seal arrangement including a first seal part surrounded by the slide pin and the boot and a second seal part provided inside the cylindrical portion of the caliper.
It has been, however, a problem with such arrangement of the conventional pin slide type brake that the air pressure in the second seal part inside the cylindrical portion increases when the brake is assembled and mounted. As shown in FIGS. 1 and 2 of the accompanying drawings, when the main slide pin 3 which is supported in a cantilever like manner by a support 2 is inserted into the cylindrical portion 6 of a caliper 5 which has one end of the cylindrical portion 6 closed, the volume of the space of the second seal part 13 which is surrounded by the slide pin 3, the cylindrical portion 6 and one end of a boot 10 comes to decrease according as the slide pin 3 is inserted. Then, since this part is shut off from the outside, the air pressure inside this part increases. The increased pressure of air then act as a force to cause a relative movement of the slide pin 3 or the support 2 and the caliper 5 and, under a non-braking condition, causes the caliper 5 to move to a certain extent in the direction of an arrow shown in FIG. 1. This in turn pushes an outer friction pad 9 against a disc rotor 1 to cause dragging there.
This problem can be solved by venting the increased portion of pressure of air to the outside by providing, for example, a check valve at the closed end of the cylindrical portion 6 of the caliper. Such arrangement, however, necessitates the provision of the check valve and an additional process of mounting the check valve and thus results in increase in the number of assembling steps as well as increase in the number of parts. Such arrangement thus causes an increase in cost. The present invention, therefore, is directed to the effective solution of the above stated problem by modifying the shapes of the slide pin and the boot without incurring such increase in cost.